From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steve Wise Subject: Re: [PATCH 09/11 v2] RDMA/cxgb4: Support on-chip SQs. Date: Wed, 29 Sep 2010 12:14:54 -0500 Message-ID: <4CA3740E.9020104@opengridcomputing.com> References: <20100913162357.20948.28267.stgit@build.ogc.int> <4CA22E84.404@opengridcomputing.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Roland Dreier Cc: linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-rdma@vger.kernel.org On 09/28/2010 10:41 PM, Roland Dreier wrote: > > We would remove it I guess. I see that mlx4 assumes > > pgprot_writecombine() exists and works correctly across all platforms. > > See mlx4_ib_mmap(). > > It might be more accurate to say that mlx4 assumes pgprot_writecombine() > is defined on all platforms. Any platform that hasn't defined it (or > where the concept of write combining doesn't make sense) just falls back > to defining it as pgprot_noncached(). > > > From a quick grep it seems that /arch/powerpc has no definition of > pgprot_writecombine() but your code seems to say that one could be > given. > > This came from the ofed version of mlx4. I assume it works. :) > > If all platforms support pgprot_writecombine() correctly, then we > > don't need ocqp_supported(). > > As I said, it's a bit tricky. All platforms get some definition of > pgprot_writecombine(), but some platforms might define it as just giving > a non-cached mapping, which might lead to dire performance (perhaps > worse than just putting the SQ in host memory). I'm not sure what the > best way to handle it is -- I suppose if you wanted to get fancy you > could do a quick benchmark on startup (if such a thing is possible). > > oof. I don't want to get that fancy. :) Seems like what I need is an arch-specific function that indicates if write combining is supported or not. Or leave the code as-is. Steve. -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html